An existing database was used to compare problem gamblers (N = 138) who presented for treatment of their gambling problem to two other groups: alcohol and/or drug addiction clients who also had a gambling problem (N = 280) or who did not have a gambling problem (N = 2178). Clients with gambling as their primary problem were more likely to be female; employed or retired; more highly educated; married, divorced, or widowed; without legal problems; and older than the other groups. They also had different patterns of recent mental health diagnoses and problematic substance use. The other problem gambling clients were more similar to the substance only clients. These findings indicate that those who present for treatment of problem gambling are a distinct subset of addiction clients who have gambling problems, and emphasize the importance of considering the reasons for seeking treatment, not just the presence of a gambling problem.